The invention relates to an electrically conductive pipette tip.
Pipette tips are used together with pipettes for dosing liquids. Pipette tips have an elongated tubular body having a bottom opening at the bottom end for the passage of fluid, and a top opening at the top end for the passage of air, and a passageway between the bottom opening and top opening. Pipette tips are releasably connected to a pipette. To accomplish this, the top opening is conventionally clamped to a mounting shaft at the bottom end of the pipette, or the top end is clamped in a blind hole in the bottom end of the pipette. The bottom end of the mounting shaft, or the blind hole in the top end, has a passage for air that is connected via a connecting channel to a displacement unit for air. The displacement unit is generally designed as a piston/cylinder unit.
By means of the displacement unit, an air column is displaced to draw liquid into the pipette tip clamped onto the mounting shaft or clamped in the blind hole, and to eject it therefrom. If the bottom opening of the pipette tip is dipped into a liquid, the aspiration stroke of the displacement unit displaces the air column away from the bottom opening, and liquid is drawn into the pipette tip. By means of the dispensing stroke of the displacement unit, the air column is displaced toward the bottom opening, and liquid is ejected out of the bottom opening of the pipette tip. The amount of drawn and released liquid depends on the stroke of the displacement unit. Fixed volume pipettes are known with an unchangeable stroke, and variable pipettes are known with an adjustable stroke.
The displacement unit can be operated manually or with a motor. In addition, the pipette can be handheld and/or operated in a stationary manner. In particular, the pipette can be integrated in a dosing station or workstation.
Pipettes for single use are made of plastic, especially polypropylene.
During the aspiration stroke, the pipette tip needs to remain permanently immersed in liquid to prevent incorrect dosage from the aspiration of air. To determine whether or not a pipette tip is immersed in liquid, there are pipette tips made of electrically-conductive plastic such as pipette tips of the LiHa Disposable Tips series (TECAN AG, Männedorf, Switzerland).
For the use of electrically conductive pipette tips, there are pipettes with an electronic device that contact a mounted pipette tip and, by measuring capacitance, determine whether the pipette tip is immersed in liquid. Frequently, pipettes in automatic dosing stations or workstations are equipped with such a device. However, in principle, also other stationary or handheld pipettes can be correspondingly equipped.
Conventionally, electrically conductive pipette tips are made of an electrically conductive polypropylene compound with conductive carbon black. Consequently, electrically conductive pipette tips are black and opaque. Therefore the user cannot visually check during use if the pipette tip contains liquid or not. In addition, the cost of electrically conductive pipette tips is comparatively high since a carbon black component has to be processed.
A liquid transfer device is known from U.S. Pat. No. 6,551,558 B1 with cannulas consisting of concentric tubes made of metal or conductive plastic with insulation therebetween for detecting immersion in liquid. The tubes made of metal or conductive plastic are opaque.
A couvette is known from US 2005/0064578 A1 that has electrodes in facing walls which form a capacitor for electroporation. The couvette is produced in a two-component injection-molding procedure.
U.S. Pat. No. 5,660,797 describes a pipette tip consisting of different materials. In particular, the inside of a collar can consist of a material that is softer than the plastic of the remaining pipette tip to improve the seal when the top edge of the pipette tip sits tightly on a pipette in a friction lock.
EP 1 607 747 A2 describes a pipette tip that has two electrically conductive areas on the outside that form a capacitor for capacitively measuring the liquid level. The capacitance of the capacitor changes with the amount of drawn liquid.
DE 44 02 654 A1 discloses a dispenser with an electrode consisting of a conductive paint applied by screen printing.
U.S. Pat. No. 5,045,286 describes a device for aspirating a certain amount of liquid that has two electrodes which are contacted by electrically conductive areas of a seat that can be pressed into their top opening. The device is created by injection molding.
Against this background, an objective of the invention is to provide an electrically conductive pipette tip with improved application characteristics. In particular, it is the objective of the invention to provide an electrically conductive tip that allows the level of the liquid to be visually inspected.